Stars are amazing luminous spheres of plasma held together by their own gravity. The nearest star to Earth, the Sun, created our solar system and gives us the light energy we need to live.
But why do stars come in different colors? The distinct coloring of stars allows astronomers to characterize different types of stars based on several different factors.
A star’s color ranges from blue-white and yellow to red and orange, mainly as a result of its temperature, distance, and composition. Stars emit light energy made up of different wavelengths which contribute to their color, and this can change over long periods of time.
How Does Temperature Affect A Star’s Color?
A main contributing factor to a star’s color is temperature. When the heat of a star rises, its overall emitted energy increases, which causes the peak of the curve to move towards shorter wavelengths.
As a star heats up, its radiated energy is forced closer to the blue end of the spectrum. When a star becomes colder in temperature, it moves closer to the red end of the spectrum. These temperature differences, therefore, affect which end of the spectrum a star is on, and therefore its color.
How Does Distance Affect A Star’s Color?
Distance affects a star’s color due to the Doppler Effect. The Doppler Effect is when the frequency of light waves increases or decreases as a result of the distance between the object and the viewer.
The light being emitted by a star far in the distance is shifted closer to the red end of the spectrum (this is known as redshift) if it is moving further away, and the light from a star moving nearer is shifted towards the blue end of the spectrum (blueshift).
How Does Composition Affect A Star’s Color?
When heated, elements give out different wavelengths of electromagnetic radiation. Stars are composed of hydrogen and helium as their main elements, alongside traces of other elements.
A star’s color is determined by the accumulation of the different wavelengths. This is called Planck’s curve. The wavelength at which a star emits the most light is called the star’s “peak wavelength” (known as Wien’s Law), which is the peak of its Planck curve.
However, how that light appears to the human eye is also mitigated by the contributions of the other parts of its Planck curve.
When different wavelengths accumulate, they are seen as white in color, which makes the color of the star lighter than where its peak wavelength actually resides on the spectrum.
The composition of a star depends on its formation so far. Each star is created from a molecular cloud of gas and dust, and each star forms differently. Stars are made mainly from hydrogen (a crucial fuel for forming stars) but they carry other elements too.
The mass and different composition elements decide the make-up of the resultant star. Spectroanalysis, which is a method used to examine the wavelengths of a star with a spectrometer, allows astronomers to decipher which elements are present in the star.
How Are Stars Classified?
Astronomers classify stars based on their individual factors, such as their color, size, brightness, and temperature.
The Morgan-Keenan system (MK) classifies the majority of stars based on temperature, using a range of letters, with O being the hottest temperature and M being the coolest temperature.
The letter class is subdivided using a range of digits with 0 being the hottest temperature and 9 being the coolest (for example, 01 would be the hottest star).
Luminosity is also added to the MK system classification using Roman numerals based on the width of absorption lines in the spectrum of the star, which changes according to atmospheric density.
This can therefore be used to determine whether a star is a giant star or a dwarf. 0 and I are the Roman numerals used to classify the luminosity of hyper or supergiants, whereas numerals II, III, and IV are used to classify the luminosity of regular and subgiants. V classifies main sequence stars, while VI and VII are used to classify subdwarfs and dwarfs.
In addition, the Hertzsprung-Russell diagram compares a star’s classification to its absolute magnitude (luminosity, intrinsic brightness, and surface temperature).
The same classification is used for types of stars, which range from the blue end of the spectrum to the red end. This is then added together with the Absolute Visual Magnitude (Mv) and placed on a two-dimensional chart.
Stars in the O class are the hottest stars and tend to be much bigger, whereas K and M class stars are normally much cooler and smaller in size.
How Does A Star’s Evolution Affect Its Color?
During different stages of a star’s formation, its size, temperature, and color vary.
It makes sense that as a star is moving through different phases of its life cycle, it reaches different temperatures, grows larger and smaller, and therefore moves towards different ends of the color spectrum.
Final Thoughts
In summary, the color of a star can change as it evolves, due to its changing temperature, its composition, and its size.
Stars’ colors can change over an exceptionally long time period. They can become very hot and move towards the blue end of the spectrum, and as they expend their nuclear fuel they can move towards the redder end, whereas others might cause a massive explosion.
There is still much we need to learn about stars, and focusing further scientific efforts on discovering the wonders of astronomy and space may help us uncover the many mysteries of the universe we call home.
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